1. The Field of the Invention
The present invention relates to methods and compositions for controlling the density of emulsion explosive compositions. More particularly, the present invention relates to the addition to such emulsion explosive compositions of a second emulsion containing an aqueous solution of hydrogen peroxide, a carbonaceous liquid, and an emulsifier.
2. Technical Background
Water-in-oil emulsion explosives are well known in the explosives art and have been demonstrated to be safe, economical and simple to manufacture. Such explosives are known to yield excellent blasting results, particularly in applications such as mining and construction. Early explosives of this nature were comprised of an aqueous discontinuous phase containing dissolved oxygen-supplying salts, a carbonaceous fuel continuous phase, and an emulsifier. It was observed that explosives comprised of these simple ingredients were less than ideally effective because they were overly dense and difficult to effectively detonate. It is preferred in the explosives industry that explosives of this type be detonable by a conventional blasting cap, i.e. the explosives are "cap sensitive." In the case of emulsion explosives of this type, it has been found that it is necessary to control the density of the explosive in order to achieve the desired performance and to provide cap sensitivity.
In order to achieve effective density control, some systems have included an occluded gas within the explosive emulsion. Occluded gases have been provided in a number of different forms and through several different mechanisms. For example, one method of providing an occluded gas is to add glass beads or micro balloons to the explosive formulation. The glass beads or micro balloons reduce the density of the explosive and also provide hot spots during detonation.
This method, however, has limitations in that a supply of glass beads and micro balloons must be maintained at the location at which the explosive is formulated. In addition, adding these materials to the explosive complicates formulation of the emulsion explosive. Using micro balloons or glass beads it is necessary to deal with uniformly mixing the explosive emulsion and the micro balloons or beads in order to achieve uniform density of the explosive.
In order to avoid some of these problems, an alternative approach has involved the addition of an ingredient which reacts in the environment of the emulsion explosive to form a gas. Foaming and gassing agents of various types are known and used in the art. Examples of such agents include peroxides, nitrites, nitrosoamines, alkali metal borohydrides, and carbonates.
Again, the use of chemical foaming or gassing agents of this type presents some significant limitations. For example, it is difficult to control the extent and timing of the gassing reaction. Thus, it is difficult to provide uniform gassing of the explosive. The result is that uniform mixing of the gassing agent and the explosive may not be achievable prior to the gassing reaction. Thus, there may be density gradients throughout the gassed explosive, rather than an explosive composition having uniform density.
One attempt to avoid some of these problems has been to provide gassing agents which include two reactive species. One of the reactive ingredients is added to the aqueous-based explosive ingredients and the other reactive ingredient is add to the oil-based ingredients. Typical ingredients of this type include acids, nitrites, urea and thiourea. Thus, when the emulsion is formed by mixing the aqueous phase and the oil phase, the ingredients react to form a gas, resulting in uniform distribution of the gas throughout the explosive emulsion.
Using this system, it is clearly necessary to maintain the oil phase and the aqueous phase separately until it is time to use the explosive since mixing the ingredients results in a gas generating reaction. Accordingly, complete mixing of the explosive emulsion must occur at the site of use and a mixer capable of forming the overall emulsion must be provided at the site. In addition, problems encountered with the creation of the base emulsion must be dealt with on site. This is a disadvantage to the use of this type of system.
Another approach to overcoming the problems encountered in uniform gassing is the formation of a separate emulsified gassing agent. The method comprises preparing an emulsion gassing agent in the form of a water-in-oil emulsion wherein the active ingredient of the gassing agent is in the discontinuous phase and adding the said emulsion gassing agent to a prepared water-in-oil emulsion explosive. The gassing agent which is, itself, a water-in-oil emulsion, is distributed through the emulsion explosive by conventional mixing or stirring methods. In such systems, the active ingredient of the gassing agent reacts with the inorganic oxidizer salt contained in the discontinuous phase of the emulsion explosive to generate small gas bubbles which are distributed throughout the emulsion explosive.
This method shows promise. However, it has been successfully demonstrated with only a very limited number of gassing agents, primarily sodium nitrite. Unfortunately, this method has not been successfully demonstrated with other powerful gassing agents.
Accordingly, it would be a significant advancement in the art to provide methods and compositions for gassing emulsion explosive compositions which overcame some of the limitations identified above. In particular, it would be an advancement in the art to provide emulsified gassing agents which were capable of using powerful gassing agents other than sodium nitrite. In particular, it would be an advancement in the art to provide such emulsified gassing agents that were capable of using peroxides as the gassing species.
Such methods and apparatus are disclosed and claimed herein.